Among the multitude of existing batteries and cells, batteries called thin film batteries are known. These batteries, shown in FIG. 1, comprise a cathode and anode separated from each other by a separator. The battery further comprises two current collectors which transport the electrons between the cathode and anode and the electric circuit outside the battery.
One of the applications of these batteries, or electrochemical devices, is to obtain flexible batteries. To achieve this, the current collectors and separator must be flexible. One of the elements which greatly limits the flexibility of thin film batteries is the current collector. The current collector is the element of the battery which must have the best electrical conductivity, since the distance travelled by the electric current is by far the greatest (along the entire dimensions of the battery, whereas in the other elements the current only travels the shortest dimension, i.e. the thickness). Too high resistance in the current collector leads to a battery voltage drop and to energy dissipating in the form of heat. For this reason, metals are generally used for the current collector since they have the best electrical conductivity among ambient temperature materials. When the current collectors take the form of metal sheets and are placed outside the battery, as in FIG. 1, they also act as barrier layers preventing the evaporation of the electrolyte and the entry of gases which are noxious for the battery (depending upon the type of battery, e.g. CO2, O2, H2).
However, very flexible materials, such as polymers or composites, can be used for the other battery elements. The use of a metal sheet as the current collector has a negative effect on the flexibility of the battery. Moreover, since the current collector is generally found at the ends of the battery, it is therefore the element that undergoes the highest curvature stress, i.e. a traction stress at the highest radius of curvature on the outside, and compression stress at the smallest radius of curvature on the inside. Consequently, cracks appear in the current collectors after around a hundred bends at radii of curvature of less than 1.5 cm. These cracks become more marked with an increasing number of bends and form folds which damage the active layers inside the battery. This results in a decrease in capacitance which becomes increasingly marked and eventually destroys the battery.
Furthermore, it is known from the prior art the documents U.S. 2007/003812 and JP 2001 250559 disclosing, respectively, a fuel cell comprising the current collectors made in an amorphous metal and a battery comprising a cathode and an anode separated between them by a separator, said battery further comprising two current collectors, the current collector of the cathode being made in a metal or amorphous alloy.